High temperature oxidative degradation resistant fluids and the preparation thereof



3322,71 Patented May 30, 11967 HIGH TEMPERATURE OXIDATIVE DEGRADA- TEUN RESISTANT FLUIDS AND THE PREPA- RATEQN THEREOF Roland E. Dollie, .lrx, Dayton, Ohio, assignor to the United States of America as represented by the Secretary of the Air Force No Drawing. Filed Oct. 6, 1964, Ser. No. 402,036

6 Ciaims. (Ci. 252-49.7)

This invention described herein may be manufactured and used by or for the United States Government for governmental purposes without the payment to me of any royalty thereon.

This invention relates to high temperature oxidative degradation resistant functional fluids such as lubricating fluids and to a novel combination of antioxidant substances therewith.

In the advancing technology of high-speed aircraft, rocket engines, aerospace vehicles and the like, the need for lubricating fluids capable of maintaining their lubricious qualities in oxidative environments, particularly at elevated temperatures, has been and continues to become more acute and critical. While the addition of various substances and combinations of substances to conventionally employed and otherwise desirable mineral oils and other predominantly aliphatic hydrocarbon fluids has provided excellent protection against oxidation at relatively low temperatures on the order of 150 Fahrenheit or less, these additives have been regarded as storage stability degradation inhibitors, the eflects of which are considerably decreased at elevated temperatures on the order of 350 Fahrenheit and above. Accordingly, to achieve the required lubricity at high temperature oxidative environments, the prior art has at least temporarily abandoned the known and proven lubricating fluids and has come up with a variety of synthetic oils which are primarily if not strictly aromatic in character. To these aromatic fluids various substances have been successfully added to impart oxidation resistance at the higher temperatures. In most if not all cases however, these newly developed fluids at both high and low temperatures lacked many of the important lubricating qualities of the conventional mineral oils and aliphatic hydrocarbon fluids.

It is accordingly an object of this invention to provide a means or system for improving the high temperature oxidative degradation resistance of conventional aliphatic natural mineral oils and synthetic aliphatic hydrocarbon fluids.

Another object of this invention is to provide functional or lubricating fluids which will maintain their lubricious characteristics through prolonged exposure at high temperatures to oxidative environments. The combination of amine and tin compounds is a novel feature of this invention.

To accomplish these and other objects and advantages which will appear from a reading of the following disclosure, the within invention is based upon the use as additives of a secondary aromatic amine compound in combination with an aromatic tin-containing compound in the aliphatic hydrocarbon fluid. While various amines have been used as storage stability inhibitors to protect against oxidation at relatively low temperatures, it has been only when such amine-s were combined with other substances that they provided any oxidation resistance at higher temperatures. The substantial improvements in high temperature oxidation resistance have been largely confined however to aromatic type fluids.

In the case of the present invention on the other hand, the addition of the combination of the amine compound and the aromatic tin-containing material has not only improved the oxidation resistance of the mineral oils and related functional lubricating fluids but also has done so to a degree that is far greater than could have been anticipated from the previously known effects of the amine compounds or of the organometallic substances used singly and not in combination with each other. This phenomenon wherein the total gain achieved by the combination of two elements exceeds the arithmetical sum of the gains of each used separately is sometimes referred to as a synergistic effect. As a result of such synergistic improvements provided by this invention, various aliphatic hydrocarbon fluids which previously lacked adequate oxidative stability at elevated temperatures may now be satisfactorily utilized in severe oxidative environments a temperatures of 400 Fahrenheit and beyond as instrument oil, gear box oil, grease base fluids and the like. Other aliphatic hydrocarbon fluids which have been utilized under limited oxidative conditions may now be used under exposure to higher oxidating potentials at temperatures of from 50 to 100 Fahrenheit beyond those that had been heretofore possible.

The aliphatic hydrocarbon base fluids of the types to which the teachings of the within invention are applicable include the straight chain and branch chain aliphatic materials. Specific base fluids within this class include mixed alkyl-substituted pyrazines and alkyl-substituted silane materials. The teachings of this invention are therefore applicable to a wide variety of synthetic or naturally occurring organic fluids containing either branched or straight-chained aliphatic molecules. Within this class of materials are 2-n-heptyl-6-(5-tridecyl)pyrazine, 2-11- heptyl-5-(S-tridecyl) pyrazine, 2- (2-octyl) -6-(2-decyl) pyrazine, Z-n-heptyl-6-n-nonylpyrazine, 2 phenoxy 3 (5- nonyl)pyrazine, 2,6,10,l4-tetramethylpentadecane and octadecyl tri-n-decyl silane. The lubricating base fluids alone are not stable under severe oxidation conditions at the high temperatures in the order of 350 F. and above, excepting when they are mixed with the amine and tin combinations that are disclosed herein.

The secondary aromatic amine component of the additive system to any of the above base fluids may be one of a variety of derivatives of ammonia in which two of the hydrogen atoms are replaced, both by an aromatic or one by an aromatic and the other by an aliphatic substituted aromatic substituent, the term aliphatic being taken here to include branched or straight-chain saturated hydrocarbons and the term aromatic to include polynuclear, cyclic, heterocyclic and other ring compounds which may or may not be substituted with aliphatic groups or other atoms. Such secondary aromatic amines are according to the formula HNR R' where R is an aromatic or aryl substituent or group, R is an aliphatic substituted aromatic group and n is one or two or zero. Two specific secondary amines within this broad class which have been found particularly adaptable for the uses and purposes of this invention are phenyl alphanaphthylamine and p,p'-dioctyldiphenylamine.

the table below; and, when these formulations were subjected to the above-described micro-oxidation tests at temperatures of 425 Fahrenheit the listed values of kinematic viscosity change and neutralization number change with the balance of its valences being satisfied by one 5 were achieved.

Kinematic Neutraliza- Wcight Viscosity tion Number Aromatic Tin Compound Percent Change at. Change 100 F. (mg. KOl'l/g.) (perccnt) Bis hcnox hen ldi hen ltin 1.0 20.0 0.6 8%.? l 2.0 13.3 0.4 Do..- 0.5 25.4 0.3

azastannine l. 0 31. 7 0. 4 Perfluorotetraphenyl 1. 0 31. 3 0. (i o 0.25 43.2 0.6

Tetraphenyltin. 0. 1 89. 2 1. 4 D0 1.0 15.3 0. 0 Do 2.0 10.8 0.7

or two saturated aliphatic groups. The structural formula for such aryl tin compounds is R SnR wherein R is an aromatic group, R is an alkyl or aliphatic group as above defined and n is an integer from one through four. Specific aryl tin compounds within this definition which have yielded the improvements sought by the present invention include bis(p-phenoxyphenyl)diphenyltin, S-ethyl S, 10-dihydro-10,10-diphenylphenazastannine, tetraphenyltin and perfluorotetraphenyltin.

The amount of each of the above types of additives to be used in particular fluid formulations varies with the oxidative stability of the base fluid, the solubility of the additive therein and other physical factors. Experimental results have indicated that some noticeable improvements are obtained where each of the additives represents as little as 0.1% of the total formulation and that the resistance of the formulation to oxidative degradation results when the percentages each or both of the additives are increased to as high as 5% by weight of the total formulation. In the usual case however each of the additives will be present in the final formulation in a weight percentage of from .25% to 1.0%. In the preparation of these fluids, the additives are added to the base fluid which is then heated and/ or stirred usually at from 180 to 212 Fahrenheit until solution is completed which usually requires on the order of five to ten minutes. Where the additives are less soluble in the particular base fluid, the heating may be increased to as high as 250 and additional mixing time may be allowed.

To demonstrate the effectiveness of the teachings of this invention, various functional fluid formulations in compliance therewith were subjected to micro-oxidation tests involving the passage of up to liters per hour of dried air through a ZO-milliliter test sample for a 24-hour period at a constant temperature. The test temperatures and air flow rates in the tests were adjusted for a particular base fluid so that under the same conditions the fluid without the additives would be severely oxidized. The criteria for determining the extent of oxidation were the percent of kinematic viscosity change at 100 Fahrenheit and neutralization number change (Mg KOI-I/g.), based upon the viscosity and neutralization number of the fluid formulation before the test.

In one set of comparative tests, 2-n-heptyl-6-(5-tridecyl) pyrazine was employed as a base fluid to which 1.0 weight percent of phenyl alpha-naphthylamine (sometimes referred to as PANA) was added along with varying weight percents of various aryl tins as illustrated in For purposes of comparison with the present invention, the pyrazine base fluid involved in the tests above was run without any secondary amine or aryl tin additives; and, at 425 Fahrenheit, the sample charred badly and only a solid residue remained. Where the same test on the unmodified fluid was run at 325 Fahrenheit, the kinematic viscosity change at 100 Fahrenheit was 63.9% and the neutralization number change was 3.4. Where the pyrazine base fluid was modified by the addition of 1 weight percent of the PANA without any aryl tin additive, the oxidation test at 425 Fahrenheit showed a kinematic viscosity change of 140% and a neutralization number change of 2.0 which are both objectionably high as compared with the present invention. At the same time, where the base fluid was modified with the addition of 1.0 weight percent of the bis(p-phenoxyphenyl)diphenyltin, .25 weight percent of the perfluorotetraphenyltin, 0.1 weight percent of tetraphenyltin and 1.0 weight percent of tetraphenyltin, without any PANA, all the samples charred badly and only solid residues remained. In other tests involving the same base fluid modified with 1.0 weight percent of the PANA and comparable amounts of non-tin containing materials of the type generally related to the aryl tin compounds but having silicon, lead or germanium moieties, the kinematic viscosity changes were from four to eight times greater than the better formulations that were made to embody this invention.

The same tests and comparisons made in connection with the combination of the secondary amine and aryl tin additives of this invention to an alkyl-substituted pyrazine base fluid such as 2-(2-octyl)-6-(2-decyl)pyrazine, 2- n-heptyl--n-nonyl pyrazine and 2-phenoxy-3-(5-nonyl) pyrazine and 2-n-heptyl-5-(5-tridecyl)pyrazine showed comparable degrees of improvement over the base fluids without any additives or with one or the other of the additives singly. So also similar tests run on synthetic high molecular weight aliphatic hydrocarbons and 2,6,10, 14-tetramethylpentadecane and octadecyl tri-n-decyl silane to which the antioxidant system of this invention had been added gave overwhelming oxidative superiority over the same base fluids without any additives or with one or the other of the additives.

Comparative experimental data for the high molecular weight hydrocarbon, pentadecane and silane formulated with varying weight percents of various aryl tins combined with either PANA or p,p'-dioctyldiphenylamine (referred to here as DODPA) are given in the three tables below:

phatic hydrocarbon structures which does not occur when v Kinematic Neutralization the secondary amine or the tin containing compounds are Addltlvfls) i 3 2 9 Weight g i g used singly (i.e., not in combination with each other) it y r c r 01 engea ange o is also demonstrated that the uncombmed additives ac- (percent) cording to this invention do not in and of themselves produce an eifective antioxidant system for aliphatic hydrof 'z QP 1 g carbons at high temperatures cen ns p-p enoxyp eny 1- 1 iiei iuinn nn 15.7 0.0 The structures for the corresponding base fluids and g g ?gig fl fi jg f jgg; additives discussed in this disclosure are given below. 1 liphzeuylpheiazgsniianigili ie165.035.. 15.8 0.0 The fOllOWillg are synthetic lubricants that at high \v percen w 8%???lpgg g ijgg g 2 0 0 :empceraturesddegdrade unless they ared clonzbinecifwith (a;

y 1 H111 in c m oun an an 31111 c i i e 1.0wt.percent PANA +1.0Wtpercent h p ne Ompoun t a are 18C OS 5'ethyl-5,10-dihydr0-10-10dipheuylerem phenazastannine.-. 15.4 0.0 p 1.0 wt. percent PANA ne-note the 15 CH3(CHZ)3 the objectionable high viscosity. 1, 380 1. 4 1.0 Wt. percent bis(p-phenoxypheiiyl) H0 2)n s diphcnyltiii 959 0. 4 H 1.0 wt. percent 5-ethyl 5,10-dihydro-10, 0 2)1 lO-diphenylpheuazastannine 134 0. 8 1.0 wgl. pizrcentdlflAlgrA 1H0 vdvt rgerceilit 5-eiy-5 O-iiy o-010- ip eny 7.. phemlzas'flme 11180 M 2 I1 n s 6 yhnr Base fluid with no additive 3,020 0. 7 N

(CH2)7CH3 CHa(CH2)3 Micro test conditions: 400 F., 20 liters/hour air rate, 0 24 hours duration.

2 CI'I3(OH2)1 Kinematic Neutralization o. .r. r. Ad(litive(s) in 2,6,10,14-Tetrametliyl- Viscosity Number n heptyl mdecynpymzme peutadccane Change at Change W 100 F. (mg.KOH/g.) l 0 (percent) i H H 1.0 Wt.pcrcent PANA +1.0 wt percent 930K! his(p pheuoxyphenyl) diphenyltiin. 0.0 0.0 H 1.0 Wt. percent PANA +1.0 wt. per- 93C 3 cent 5-ethyl-5,10-dihydro-10,10-dipheiiylphenazastannine 0. 0 0. 4 2-phenoxy-3-( fi-nonynpynazine 1.0 Wt. percent PANA +1.0 wt. percent triphenylzltglgltrinx. Hunt. 0 0. 1 N 1.0 Wt. percen 5 w per- H cent tetracyclohexytin. 2.0 0.3 CH3: m (CHMCHB 1.0 wt. percent DODPA 1.0 wt. percent PANA submitted for contrast since it does not work because of the resultingf lilgh viscosity w ich is a so true 0 ie her we formulations 2 00 37.1 P Y Y 1 37 1.0 Wt. percent bis(p phenoxyphenyl) diphenyltin CH3(CH2)7 (CHmCI-I; 1.0 wt. percent PANA +1.0 wt. percent 5-ethy1-5,10-dihydro-10,10-di- 0- CH phenylphcnazasiline. 1,910 28. 4 Base fluid CH3 CH3 N/ 1 Barely fluid at room temp. 2 Not fluid at room temperature. 12 (2.0946371) 6.(2 decy1)pyrazine Micro test conditions: 400 F., 20 liters/hour air rate, CH3 24 hours duration. I

M Kinematic Neutralization CH3 C Hz) Si(C Hz) 17CH3 Viscosity Number Additive(s) in Octadeeyl Change at Change M Tri-n-Dccyl Silaiie 100-F. (mg. KOH/g.) I

(percent) H3 1.0 wt. yiaercenthPANA {llonv it. lp Oc'tudecyl trru decyl silaue cent is p-p enoxyp ieuy (1p entin ngifix pinnt. 64.9 1.3 I E B I a 1.0 Wt. ercen i .0 w ercent p 5-ethyl-5,10- lihydro-10,1(i dia 2) 2)S a phenylphenazastaunine 54. 2 1. 1 Percent DODPA 2,6,10,14-tetrainethylpentadecane percent1 5ethyl-5.10-dihydi'0-10,10- 10 1 dipheny phenazastanniue .9 0. 10 wt percent PANA for Contrast it The following additives have been found useful in acdoes not work satisfactorily, nor do cordance With my invention: the next three (3) formulations which also are submitted for contrast 610 5. 6 EN 1.0 wt. percent bis(p-phenoxyphenyl) diphcnyltin 3,610 0.2 1.0 Wt. percent tetraphenylgcrinaniilin 1, 980 2. 7 1.0 wt. percent DANA 1.0 wt. percent 5-ethyl-5, 10-diliydro-10,10-diphenylpheuazasiiine 945 0, 1.0 wt. percent PANA 1.0 Wt. percent tetrapliei'iylgerinanium 1, 136 7. 4 Base fluld 2520 Phenyl ulpha-naphthylamine Micro test conditions: 425 F., 10 liters/hour air rate, 24 hours duration. crr3 om 7-i r(cin)7cn3 While these tests demonstrate that a synergistic effect is produced strongly inhibiting the oxidation of the alipypI Dioctyldiphenylamine CzHs -ethyl 5,10-dihydr0-10,10diphenylphenazastannine F F F Perfiuorotetraphenyltin Bis (pphen0xyphenyl) diphenyltin While the foregoing invention has been described in considerable detail in connection with certain specific examples and embodiments thereof, it is to be understood that the foregoing particularization has been for the purposes of illustration only and does not limit the scope of the invention as it is defined in the subjoined claims.

I claim: 1. A lubricant resistant to oxidation at high temperatures on the order of 350 F. comprising (a) a base fluid in an amount of about 95 to 99.9% by weight selected from the group consisting of 2-n- 'heptyl 6 (S-tridecyDpyrazine, Z-n-heptyl-S-(S-tridecyl pyrazine, 2- (2-octyl) -.6- (Z-decyl pyrazine, 2-nheptyl-6-n-nonylpyrazine, 2-phenoxy 3 (S-nonyl) 8 pyrazine, octadecyl tri-n-decylsilane, and 2,6,10,14- tetramethylpentadecane;

(b) an amine additive combination selected from the group consisting of phenyl-alpha-naphthylamine and p,p-dioctyldiphenylamine; and

(c) aryl tin compounds selected from the group consisting of tetraphenyltin, perfluorotetraphenyltin, bis- (p-phenoxyphenyl diphenyltin, and S-ethyl-S, lO-dihydro-10,10-diphenylphenazastannine.

2. The lubricant of claim 1 in which the amine and aryl tin compound are each present in the amount of .l% to 5% by weight.

3. The lubricant of claim 2 in which the amine and aryl tin compound are each present in the amount of 25% to 1% by weight.

4. A lubricant resistant to oxidation at high temperatures on the order of 350 F. consisting essentially of (a) a base fluid in an amount of about to 99.9% by weight selected from the group consisting of Z nheptyl 6 (5-tridecyl)pyrazine, Z-n-heptyl-S-(S-tridecyl)pyrazine, 2-(2-octyl)-6-(2-decyl)pyrazine, 2-nheptyl-6-n-nonylpyrazine, Z-phenoxy 3 (S-nonyl) pyrazine, octadecyl tri-n-decylsilane, and 2,6,10,14- tetramethylpentadecane;

(b) an amine additive combination selected from the group consisting of phenyl-alpha-naphthylamine and p,p-di0ctyldiphenylamine; and

(c) aryl tin compounds selected from the group consisting of tetraphenyltin, perfluorotetraphenyltin, bis- (p-phenoxyphenyl)diphenyltin, and 5-ethyl-5,l0-dihydro-10,10-diphenylphenazastannine.

5. The lubricant of claim 4 in which the amine and aryl tin compound are each present in the amount of .l% to 5% by weight.

6. The lubricant of claim 5 in which the amine and aryl tin compound are each present in the amount of 25% to 1% by weight.

References Cited UNITED STATES PATENTS 2,160,911 6/1939 Russell 252-49] 2,165,324 7/1939 Wiezevich et al 25249.7 2,930,758 3/1960 Tierney et al 25249.9 3,036,005 5/1962 Koch 252400 3,079,414 2/1963 Tamborski et al. 25249.7

OTHER REFERENCES Synthetic Lubricants, Gunderson et :a1., Reinhold Pub. Corp, New York, 1962, pp. 464-474, 482-487.

DANIEL E. WYMAN, Primary Examiner.

L. G. XIARHOS, W. H. CANNON, Assistant Examiners. 

1. A LUBRICANT RESISTANT TO OXIDATION AT HIGH TEMPERATURES ON THE ORDER OF 350*F. COMPRISING (A) A BASE FLUID IN AN AMOUNT OF ABOUT 95 TO 99.5% BY WEIGHT SELECTED FROM THE GROUP CONSISTING OF 2-NHEPTYL - 6 - (5-TRIDECYL)PYRAZINE, 2-N-HEPTYL-5-(5-TRIDECYL)PYRAZINE, 2-(2-OCTYL)-6-(2-DECYL)PYRAZINE, 2-NHEPTYL-6-N-NONYLPYRAZINE, 2-PHENOXY - 3 - (5-NONYL) PYRAZINE, OCTADECYL TRI-N-DECYLSILANE, AND 2,6,10,14TETRAMEHTYLPENTADECANE; (B) AN AMINE ADDITIVE COMBINATION SELECTED FROM THE GROUP CONSISTING OF PHENYL-ALPHA-NAPHTHYLAMINE AND P,P''-DIOCTYLDIPHENYLAMINE; AND (C) ARYL TIN COMPOUNDS SELECTED FROM THE GROUP CONSISTING OF TETRAPHENYLTIN, PERFLUOROTETRAPHENYLTIN, BIS(P-PHENOXYPHENYL)DIPHENYLTIN, AND 5-ETHYL-5,10-DIHYDRO-10,10-DIPHENYLPHENAZASTANNNINE. 